The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A continuously variable transmission (“CVT”) typically includes gearing that operatively couples a variator between a rotary power source, such as an engine or electric motor, and a final drive unit. The variator includes a rotary input disk and a rotary output disk which are able to steplessly or continuously vary the ratio of an input speed to an output speed (the “variator ratio”). The overall speed ratio provided by the CVT is a function of the variator ratio and the associated gearing. The output disc includes integrally formed gear teeth that are in mesh with and drive a corresponding gear. The gear in turn is functionally coupled to an output shaft or layshaft that is functionally coupled to the final drive unit. Another type of stepless transmission includes the infinitely variable transmission (IVT). The IVT is similar to the CVT in that an engine drives the variator input discs while a layshaft takes the drive from the variator via a metal belt or gears. However, while a typical CVT includes a starting device such as a launch clutch, a typical IVT uses a gear system to provide launch from rest.
CVT and IVT designs are optimized to minimize axial length and mass. Accordingly, the gearing on the output disc of the variator has minimized gear teeth face width in order to minimize the axial length of the CVT/IVT. In addition, this gearing is often designed with a low helix angle in order to minimize variator thrust loads and thus enable small bearings and provide a more compact variator system. The combination of narrow face width and low helix angle may lead to the gear pair to have an insufficient contact ratio. This in turn places the gear pair at a higher risk for noise and strength concerns.
One solution to the above problems is to increase the width of the variator disk (i.e. the gear width). However, this will increase the variator axial length, mass, and may require the variator radius to increase as well. Another solution is to increasing the helix angle of the gear teeth on the variator disc. However, this will increase the thrust load thus requiring more axial length due to the need for stronger bearing support.
Therefore, there is a need in the art for a variator output gear set that provides adequate contact ratio while minimizing variator axial length and mass.